Method for controling air flow rate of air conditioning system

ABSTRACT

Method for controlling an air flow rate of an air conditioning system, including the steps of measuring a concentration of volatile organic compounds in air periodically, calculating a value of concentration change from concentration values measured at the present time and in the past, and controlling the flow rate of air for cleaning or ventilating a room with reference to the present concentration and value of concentration change, whereby controlling a flow rate of room cleaning or ventilating air to cope, not only with concentration of organic compounds, but also with rapid change of the concentration of the organic compounds in the air.

This application claims the benefit of the Korean Application No.P2004-0004152 filed on Jan. 20, 2004, which is hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to air conditioning systems, and moreparticularly, to a method for controlling an air flow rate of an airconditioning system, in which a flow rate of room cleaning orventilating air is controlled to cope, not only with concentration oforganic compounds, but also with rapid change of the concentration ofthe organic compounds in the air.

2. Background of the Related Art

The air conditioning system is an apparatus for maintaining room air ata most proper state according to use or purpose of the air, inclusive ofair conditioners, air cleaners, ventilating devices. The air conditionercools or heats the room by using a property of the refrigerant in whichthe refrigerant discharges or absorbs heat to/from an environment whenthe refrigerant undergoes a phase changes.

The air cleaner draws air from the room, removes foreign matters, suchas dusts, from the air, and supplies cleaned air to the room again, andthe ventilating device discharges room air to an outside of the room anddraws outdoor air into the room.

In the meantime, recently, above three kinds of devices are provided asone air conditioning system, rather than provided as independentdevices. In general, such an air conditioning system cleans room airwhile cooling/heating the room so as to keep a room temperature withinan appropriate temperature range. However, since the air of a shut tightroom is polluted gradually as time goes by, the air conditioning systemventilates the room periodically, to supply fresh air to the room.

In above process, an air flow rate of the air supplied to the room afterbeing cooled/heated and cleaned by the air conditioning system is ingeneral controlled according to a room temperature, and an air flow rateof the air supplied to/discharged from the room in ventilation iscontrolled to be constant.

However, since the foregoing typical air conditioning system isoperative only taking the room temperature into account without a levelof air pollution of the room, the air conditioning system fails toreflect very important factors, such as the level of pollution of theroom air, and a rate of pollution of the room air, to the operation.

Moreover, in a case the room air is polluted rapidly due to variousreasons, such as someone in the room smokes, or many persons use theroom suddenly, or the like, typical air conditioning system can not dealwith the change of room air, appropriately.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a method forcontrolling an air flow rate of an air conditioning system thatsubstantially obviates one or more of the problems due to limitationsand disadvantages of the related art.

An object of the present invention is to provide a method forcontrolling an air flow rate of an air conditioning system, which candeal with a level of room air pollution, and sharp change of thepollution level, appropriately.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent to thosehaving ordinary skill in the art upon examination of the following ormay be learned from practice of the invention. The objectives and otheradvantages of the invention will be realized and attained by thestructure particularly pointed out in the written description and claimshereof as well as the appended drawings.

To achieve these objects and other advantages and in accordance with thepurpose of the present invention, as embodied and broadly describedherein, the method for controlling an air flow rate of an airconditioning system, includes the steps of (a) measuring a concentrationof volatile organic compounds in air, periodically, (b) calculating avalue of concentration change from concentration values measured at thepresent time and in the past, and (c) controlling the flow rate of airfor cleaning or ventilating a room with reference to the presentconcentration and value of concentration change.

The value of concentration change in the step (b) is a difference of aconcentration value measured at the present time and a concentrationvalue measured right before. The flow rate of the air for cleaning orventilating a room includes a highest flow rate, a high flow rate, amedium flow rate, and a lowest flow rate.

Preferably, the flow rate of the air for cleaning or ventilating a roomis controlled to be the highest flow rate when the concentration valueis high, and the value of concentration change is high or medium, andthe high flow rate when the concentration value is high, and the valueof concentration change is low, or the concentration value is medium,and the value of concentration change is high.

Preferably, the flow rate of the air for cleaning or ventilating a roomis controlled to be the medium flow rate when the concentration value ismedium, and the value of concentration change is medium or low, or theconcentration value is low, and the value of concentration change ishigh, and the lowest flow rate when the concentration value is low, andthe value of concentration change is medium of low.

In the meantime, the flow rate of the air for cleaning the room iscontrolled by controlling a rotation speed of a fan which draws air fromthe room and discharges the air to the room, again. The flow rate of theair for ventilating the room is controlled by controlling a rotationspeed of a fan which draws outdoor air and discharges the outdoor air tothe room, or a rotation speed of a fan which draws room air anddischarges the room air to an outside of the room.

In the meantime, the step (c) includes the steps of (c1) determining alevel of the concentration value measured at the present time, (c2)determining a level of the value of the concentration change calculatedat the present time, and (c3) controlling a rotation speed of at leastone of a first fan for supplying air to the room and a second fan fordischarging air from the room with reference to the levels of theconcentration value and the value of the concentration change.

The step (c1) includes the step of comparing the measured concentrationvalue to various reference values, and the step (c2) includes the stepof comparing the calculated value of concentration change to variousreference values. The first fan and the second fan rotate at one ofspeeds inclusive of a highest speed, a high speed, a medium speed, and alowest speed, respectively.

The (c3) step may include the step of rotating at least one of the firstfan and the second fan at the highest speed when the concentration valueis high, and the value of the concentration change is high or medium.

The (c3) step may include the step of rotating at least one of the firstfan and the second fan at the high speed when the concentration value ishigh, and the value of the concentration change is low.

The (c3) step may include the step of rotating at least one of the firstfan and the second fan at the high speed when the concentration value ismedium, and the value of the concentration change is high.

The (c3) step may include the step of rotating at least one of the firstfan and the second fan at the medium speed when the concentration valueis medium, and the value of the concentration change is medium or low.

The (c3) step may include the step of rotating at least one of the firstfan and the second fan at the medium speed when the concentration valueis low, and the value of the concentration change is high.

The (c3) step includes the step of rotating at least one of the firstfan and the second fan at the lowest speed when the concentration valueis low, and the value of the concentration change is medium or low.

It is to be understood that both the foregoing description and thefollowing detailed description of the present invention are exemplaryand explanatory and are intended to provide further explanation of theinvention claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention.

In the drawings;

FIG. 1 illustrates a diagram of an air conditioning system,schematically;

FIG. 2 illustrates a block diagram showing relation between a controlpart and units of the air conditioning system in FIG. 1, schematically;

FIG. 3 illustrates a flow chart showing the steps of a method forcontrolling a flow rate by the control part of the air conditioningsystem in FIG. 1 in accordance with a first preferred embodiment of thepresent invention; and

FIG. 4 illustrates a flow chart showing the steps of a method forcontrolling a flow rate by the control part of the air conditioningsystem in FIG. 1 in accordance with a second preferred embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. In describing the embodiments, identical parts will be giventhe same names and reference symbols, and repetitive description ofwhich will be omitted. FIG. 1 illustrates a diagram of an airconditioning system, schematically.

Referring to FIG. 1, there is an indoor unit 10 installed on a ceilingof a room so as to be in communication with a room. The indoor unit 10includes an expansion device (not shown) for expanding refrigerant, anindoor heat exchanger (not shown) for making the expanded refrigerant toheat exchange with the room air, and an indoor fan (not shown) fordrawing the room air into the indoor unit 10, and supplying the room airto the room again via the indoor heat exchanger.

Though not shown, the indoor unit 10 has a filter assembly providedtherein. The filter assembly 10 removes foreign matters from the roomair drawn into the indoor unit 10. Accordingly, the room air 10, notonly cools or heats the room, but also serves as an air cleaner forcleaning the room air.

Moreover, referring to FIG. 1, there is an outdoor unit 20 on anoutdoor. The outdoor unit 20 includes a compressor (not shown) forcompressing refrigerant, an outdoor heat exchanger (not shown) formaking the compressed refrigerant to heat exchange with outdoor air tocondense the refrigerant, and an outdoor fan 21 for blowing outdoor airto the outdoor heat exchanger.

When the outdoor unit 20 and the indoor unit 10 are put into operation,the room air is drawn into the indoor unit, heat exchange at the indoorheat exchanger, and supplied to the room again. According to this, theroom is cooled or heated. Along with this, since the air drawn into theindoor unit 10 is cleaned by the filter assembly (not shown), the roomair is cleaned.

In the meantime, there are a plurality of air discharge ports 51 and airsupply ports 41 on the ceiling at places distanced away from the indoorunit 10. The air discharge port 51 has an air discharge duct 50connected thereto, and the air supply port 41 has the air supply duct 40connected thereto. Each of the air supply ducts 40, and the airdischarge ducts 50 has one end in communication with an outdoor.

There is a pre-heat exchanger 60 at a middle of the air supply duct 40and the air discharge duct 50 for making the room air and the outdoorair to cross and heat exchange indirectly. The pre-heat exchanger 60 hasat least one flow passage 61 in communication with the air supply duct40 for flow of outdoor air, and at least one second flow passage 62 incommunication with the air discharge duct 50 for flow of the room air.The first flow passage 61 and the second flow passage 62 are arranged tobe in contact, or cross with each other. Therefore, the outdoor air andthe room air heat exchange indirectly without mixed with each other whenthe outdoor air and the room air pass the pre-heat exchanger 60.

In the air conditioning system in FIG. 1, the air supply duct 40 and theair discharge duct 50 have an air supply fan 45 for supplying outdoorair to the room, and an air discharge fan 55 for discharging room air toan outside of the room, respectively. As shown in FIGS. 1 and 2, turnon/off and rotation speeds of the air supply fan 45 and the airdischarge fan 55 are controlled by the control part 30.

Upon putting the air discharge fan 55 and the air supply fan 45 intooperation, the outdoor air is introduced into the room through the airsupply duct 40 and the air supply port 41, and the room air isdischarged to an outside of the room through the air discharge duct 50and the air discharge port 51. In this instance, because the outdoor airis introduced into the room after having a portion of thermal energy ofthe room air discharged to outside of the room transferred thereto, aheat loss caused at the time of ventilation is reduced.

In the meantime, polluted stagnant room air contains much volatileorganic compounds, and give harmful influences to persons living in theroom, such as diseases of the respiratory organs, allergic skindiseases, headache, and the like. For prevention of this, it is requiredto measure a pollution level of the room air, and control an air flowrate of the cleaning or ventilating air based on the data.

For this, the air conditioning system of the present invention includesa VOC sensor 15. As shown in FIGS. 1 and 2, the VOC sensor 15 isconnected to the control part 30 electrically. Therefore, the VOC sensor15 measures a content of the volatile organic compounds in the room air,and transmits the information to the control part 30.

Then, the control part 30 controls the indoor unit 10, the air supplyfan 45, the air discharge fan 55 respectively based on the informationfrom the VOC sensor 15, for controlling a flow rate of the cleaning, orventilating air, i.e., supplied to/discharged from the room. A methodfor controlling a flow rate in accordance with a first preferredembodiment of the present invention will be described with reference toFIG. 3.

The control part 30 controls the air flow rate of the cleaning orventilating air when the air conditioning system is set to be operativeautomatically. When the air conditioning system starts automaticoperation, the VOC sensor 15 is stabilized for proper performance of thefunction. The stabilization of the VOC sensor 15 requires a certain timeperiod, for an example, three minutes. Therefore, the control part 30determines pass of a time period required for stabilization of the VOCsensor 30. (S1 step)

As a result of the determination, if the time period required forstabilization of the VOC sensor 15 is not passed yet, the control part30 keeps checking pass of the time period. However, as a result of thedetermination, if the time period is passed, the control part 30 reads avalue measured at the VOC sensor 15. (S2 step).

In the meantime, in general the VOC sensor 15 outputs a voltageproportional to a measured content of the volatile organic compounds.Therefore, the control part 30 determines a content of the volatileorganic compounds in the room air with reference to the voltage from theVOC sensor 15. In this instance, for determination that how muchvolatile organic compound is contained in the room air, the control part30 uses a few reference values, i.e., reference voltages, as follows.

At first, the control part 30 determines if the voltage from the VOCsensor 15 is higher than a first reference voltage, for an example, 3V.(S3 step)

As a result of this, if the voltage is higher than 3V, the control part30 determines that the air contains much volatile organic compounds.According to this, the control part 30 controls the indoor unit 10, theair supply fan 45, or the air discharge fan 55, to maximize the flowrate of air supplied to or discharged from the room for cleaning orventilating the room. (S4 step).

In this instance, when the control part 30 controls the indoor fan (notshown) of the indoor unit 10 to rotate at a maximum speed, the flow rateof air supplied to the room again after cleaned at the indoor unit 10becomes the maximum. If the control part 30 controls the air supply fan45 to rotate at a maximum speed, the flow rate of the fresh air suppliedto the room becomes the maximum, if the control part 30 controls the airdischarge fan 55 to rotate at the maximum speed, the flow rate of theair discharged to an outside of the room becomes the maximum. In a casethe control part 30 controls the air supply fan 45 or the air dischargefan 55, it is preferable that the control part 30 controls both the airsupply fan 45 and the air discharge fan 55 at the same time foreffective ventilation.

In the meantime, if the voltage from the VOC sensor 15 is lower than 3V,the control part 30 determines if the voltage is higher than a secondreference voltage, for an example, 2V. (S5 step).

As a result of the determination, if the voltage is higher than 2V, thecontrol part 30 determines that the air has an ordinary content of thevolatile organic compounds. According to this, the control part 30controls the indoor unit 10, the air supply fan 45, or the air dischargefan 55, to set the flow rate of air supplied to or discharged from theroom for cleaning or ventilating the room to medium. (S6 step).

Opposite to this, if the voltage is lower than 2V, the control part 30determines that the air has a low content of the volatile organiccompounds. According to this, the control part 30 controls the indoorunit 10, the air supply fan 45, or the air discharge fan 55, to minimizethe flow rate of air supplied to or discharged from the room forcleaning or ventilating the room. (S7 step).

For reference, the flow rate of the air supplied to or discharged fromthe room for cleaning, or ventilating the room according to the measuredvalue by the VOC sensor 15 is as shown in the following table 1. TABLE 1A method for controlling an air flow rate in accordance with a firstpreferred embodiment of the present invention. Measured VOCconcentration Air flow rate Higher than 3.0 V Maximum Below 3.0 V higherthan 2.0 V Medium Below 2.0 V Minimum

In the meantime, the control part 30 repeats a process of reading ameasured value of the VOC sensor 15, and controlling the flow rate forcleaning or ventilating the room with reference to the measured valueperiodically during the air conditioning system is operatedautomatically. For this, upon finishing above process, the control part30 determines the air conditioning system of being operated in anautomatic operation mode. (S8 step).

As a result of the determination, if the air conditioning system is notin the automatic operation mode, i.e., operated manually, or stationary,the control part 30 terminates control of the flow rate required forcleaning or ventilating the room.

Opposite to this, as a result of the determination, if the airconditioning system is in the automatic operation mode, the control part30 determines pass of the preset time period after reading the measuredvalue from the VOC sensor 15. (S9 step)

If the preset time period is passed, the control part 30 reads themeasured value from the VOC sensor 15 again, and performs above stepsstarting from the S2 step again. However, if the preset time period isnot passed, the control part 30 repeats the S8 step and the S9 stepuntil the preset time period passes.

Thus, the air conditioning system automatically controls the flow rateof the air supplied to or discharged from the room, i.e., flow rate ofthe cleaning, or ventilating air according to the content of thevolatile organic compounds in the room air. Accordingly, the firstembodiment of the present invention, the air conditioning system, notonly controls the room air temperature, but also cleans or ventilatesthe room with reference to a level of pollution of the room air, to makethe room more comfortable.

However, even if the flow rate of the cleaning, or ventilating air iscontrolled according to the content of the volatile organic compounds inthe room air, the air conditioning system has a limitation in that rapidpollution of the room air can not be dealt with, effectively. That is,the air conditioning system has a limitation in that it is difficult tosense and deal with the rapid pollution of the room air caused bysmoking or sudden increase of persons in the room.

Therefore, the present invention suggests an improved method forcontrolling an air flow rate in accordance with a second preferredembodiment of the present invention, that can overcomes the limitation.In the second embodiment that overcomes the limitation of the firstembodiment, for controlling the air flow rate of the air conditioningsystem, not only an absolute concentration of the volatile organiccompound contained in the room air, but also change of the concentrationof the volatile organic compound per unit time period are taken intoaccount.

Therefore, according to the method for controlling an air flow rate inaccordance with a second preferred embodiment of the present invention,the control part 30 can determine rapid pollution or depollution of thepresent room air through the change of concentration, to enable to dealwith the rapid pollution of the room air effectively. A method forcontrolling an air flow rate in accordance with a second preferredembodiment of the present invention will be described in detail, withreference to FIG. 4.

At first, when automatic operation is started, the VOC sensor 15 isstabilized. Of course, the VOC sensor 15 may perform the stabilizationas soon as the air conditioning system is put into operation. Then, passof a time period required for stabilization of the VOC 15 is determined.(S 10 step).

As a result, if the time period required for stabilization is passed,the VOC sensor 15 measures concentration of a content of the volatileorganic compounds in the air, periodically. Then, a value dV ofconcentration change is calculated from concentration values measured atthe present time and in the past. (S20) Since the concentration of thevolatile organic compounds is measured periodically, the value dV ofconcentration change is defined as a difference of the concentrationvalue measured presently, and the concentration value measured rightbefore.

Thus, once the concentration of the volatile organic compounds in theair is measured, and the value of concentration change dV is calculated,the control part 30 controls at least one of the measured concentrationvalue, and flow rate of the air supplied to or discharged from the roomfor cleaning, or ventilating the room with reference to the value dV ofthe concentration change.

For this, the control part 30 controls rotation speeds of the fan (afirst fan) for supplying air to the room, and the fan (a second fan) fordischarging air from the room. The first fan can be defined as at leastone of the indoor fan (not shown) provided to the indoor unit 10 and theair supply fan 45 provided to the air supply duct 40.

If the first fan is defined as the indoor fan, the control part 30controls the flow rate of the air drawn into the indoor unit 10, cleanedat the filter assembly, and supplied to the room again in air cleaning.Opposite to this, if the first fan is defined as the air supply fan 45,the control part 30 controls the flow rate of the outdoor air suppliedto the room through the air supply duct 40 in ventilation.

In the meantime, though the air conditioning system can perform the stepof cleaning or ventilating the room independently, the air conditioningsystem can perform the steps of cleaning and ventilating the room at thesame time. Accordingly, it may be defined that the first fan means boththe indoor fan and the air supply fan 45.

In this case, the control part 30 cleans the room air as well asventilates the room air, during which steps the control part 30 controlsrotation speeds of the indoor fan and the air supply fan 45 at the sametime with reference to the concentration of the volatile organiccompounds and the value dV of concentration change.

Next, the second fan can be defined as the air discharge fan 55 on theair discharge duct 50. According to this, by controlling the rotationspeed of the air discharge fan 55 with reference to the concentrationand the value dV of concentration change, the control part 30 cancontrol the flow rate of the air discharged to an outside of the roomthrough the air discharge duct 50 in ventilation.

In the meantime, the control part 30 controls the flow rate of the airsupplied to or discharged from the room for cleaning or ventilating theroom as shown in [Table] with reference to the measured concentrationand the value dV of concentration change. For reference, the flow ratefor cleaning or ventilating the room includes a highest flow rate, ahigh flow rate, a medium flow rate, and a lowest flow rate. TABLE 2 Amethod for controlling an air flow rate according to an improvedembodiment of the present invention. Concentration value V of VOC High(higher Medium Low than (over 2.0 V (below 3.0 V) below 3.0 V) 2.0 V)Value dV of High Highest High flow Medium concentration (higher than+0.1) flow rate rate flow rate change of VOC Medium Highest MediumLowest (over −0.1 flow rate flow rate flow rate below +0.1) Low Highflow Medium Lowest (below −0.1) rate flow rate flow rate

Referring to [Table 2], if the concentration value of the volatileorganic compounds is high, and the value of the concentration change ishigh or medium, the control part 30 determines that room is, not alsopolluted much presently, but also rapidly being polluted presently.According to this, the control part 30 controls such that the flow ratefor cleaning or ventilating the room is set to the highest flow rate.

If the concentration value of the volatile organic compounds is high,and the value of the concentration change is low, the control part 30determines that room is not being rapidly polluted presently, eventhough polluted much presently. If the concentration value of thevolatile organic compounds is medium, and the value of the concentrationchange is high, the control part 30 determines that room is beingrapidly polluted presently, even though polluted not so much presently.Accordingly, in above two cases, the control part 30 controls such thatthe flow rate for cleaning or ventilating the room is set to a high flowrate.

If the concentration value of the volatile organic compounds is medium,and the value of the concentration change is medium or low, or theconcentration value of the volatile organic compounds is low, and thevalue of the concentration change is high, the control part 30determines that room is polluted slightly presently, and a pollutionrate is increasing gradually presently. Accordingly, in those cases, thecontrol part 30 controls such that the flow rate for cleaning orventilating the room is set to a medium flow rate.

Lastly, if the concentration value of the volatile organic compounds islow, and the value of the concentration change is medium or low, thecontrol part 30 determines that room is clean presently, and not rapidlybeing polluted presently. According to this, the control part 30controls such that the flow rate for cleaning or ventilating the room isset to the lowest flow rate.

In the meantime, referring to [Table 2], for controlling the air flowrate according to the concentration value of the volatile organiccompounds, and the value of the concentration change, the control part30 determines a level of the concentration value of the volatile organiccompounds measured at the VOC sensor 15 and a level of the value of theconcentration change calculated presently.

The level of the concentration value is determined by comparing theconcentration value measured at the VOC sensor 15 to various referencevalues set in advance. The value of the concentration change is alsodetermined by comparing the value of concentration change calculatedpresently to various reference values set in advance.

Once the concentration value and the value of concentration change aredetermined by above method, the control part 30 controls at least one ofrotation speed of the first fan for supplying air to the room and thesecond fan for discharging air from the room, to control the flow rateof the air for the cleaning or ventilating the room. In this instance,each of the first fan and the second fan is rotated in one of variousspeeds inclusive of the highest speed, high speed, medium speed, andlowest speed.

When the first or second fan is rotated at the highest speed, the flowrate for cleaning or ventilating the room becomes the highest flow rate,and when the first or second fan is rotated at the high speed, the flowrate for cleaning or ventilating the room becomes the high flow rate.When the first or second fan is rotated at the medium speed, the flowrate for cleaning or ventilating the room becomes the highest flow rate,and when the first or second fan is rotated at the lowest speed, theflow rate for cleaning or ventilating the room becomes the lowest flowrate.

The flow chart in FIG. 4 shows the steps of a process for determininglevels of the concentration value and the value of concentration changeof the volatile organic compounds, and determining an air flow rateaccording to a result of the level determination, well. The air flowrate process will be described in more detail with reference to FIG. 4.

At first, the control part 30 determines if the present concentrationvalue is higher than a first reference value, for an example, 3V, fordetermining a level of the concentration value of the volatile organiccompounds. (S30). As a result of this, if the present concentrationvalue is higher than the first reference value, the control part 30determines that the present concentration value is high.

Once the level of the present concentration value is determined to behigh in the step S30, the control part 30 determines a level of a valueof concentration change at the present time. For this, the control part30 determines if the calculated present value dV of the concentrationchange is higher than a third reference value, for an example, +0.1.(S31) As a result, if the present value dV of the concentration changeis higher than the third reference value, the control part 30 determinesthat the level of the present value of the concentration change is high.

However, as a result of determination in the step S31, if the presentvalue dV of the concentration change is not higher than the thirdreference value, the control part 30 determines if the present value dVof the concentration change is higher than a fourth reference value, foran example, −0.1V. (S32) As a result, if the present value dV of theconcentration change is higher than the fourth reference value, thecontrol part 30 determines that the present value dV of theconcentration change is medium.

In the meantime, referring to [Table 2], if the present concentrationvalue is high, and the present value dV of concentration change is highor medium, the control part 30 determines the flow rate of the air forcleaning or ventilating the room to be the highest flow rate. In thiscase, the control part 30 rotates at least one of the first fan and thesecond fan at the highest speed. (S71)

If the present value dV of concentration change is determined to belower than the fourth reference value in the step S32, the control part30 determines the value of the concentration change is low even if thepresent concentration value is high. According to this, as shown in FIG.4 and [Table 2], the control part 30 rotates at least one of the firstfan and the second fan at a high speed for having the high flow rate.

If the present concentration value is lower than the first referencevalue in the step S30, the control part 30 determines if the presentconcentration value is higher than the second reference value fordetermining the level of the present concentration value. (S40) As aresult of this, if the present concentration value is higher than thesecond reference value, the control part 30 determines the presentconcentration value of being medium.

Then, the control part 30 determines if the present value ofconcentration change is higher than the third reference value, i.e.,+0.1, for determining a level of the present value of concentrationchange. (S50). As a result of this, if the present value ofconcentration change is higher than the third reference value, thecontrol part 30 determines that the present value of the concentrationchange is high while the present concentration value is medium.

Accordingly, in this case, as shown in FIG. 4 and [Table 2], the controlpart 30 rotates at least one of the first fan and the second fan to havethe high flow rate. (S72).

In the meantime, if it is determined that the present value ofconcentration change is lower than the third reference value in the stepS50, the control part 30 determines if the present value of theconcentration change is higher than the fourth reference value, i.e.,−0.1 for determining a level of the present value of the concentrationchange. (S60)

As a result of this, if the present value of concentration change ishigher than the fourth reference value, the control part 30 determinesthat the present concentration value is medium, and the present value ofconcentration change is medium. Opposite to this, as a result of thedetermination, if the present value of concentration change is lowerthan the fourth reference value, the control part 30 determines that thepresent concentration value is medium, and the present value ofconcentration change is low.

According to this, in this case, as shown in [Table 2] and FIG. 4, thecontrol part 30 rotates at least one of the first fan and the second fanat a medium speed to output a medium flow rate. (S73)

In the meantime, if it is determined that the present concentrationvalue is lower than the second reference value as a result ofdetermination in the step S40, the control part 30 determines that thepresent concentration value is low. Then, for determining the level ofthe present value of concentration change, the control part 30determines if the present value of concentration change is higher thanthe third reference value, i.e., +0.1. (S41)

As a result of this, if the present value of concentration change ishigher than the third reference value, the control part 30 determinesthat the present value of concentration change is high while the presentconcentration value is low. According to this, as shown in [Table 2] andFIG. 4, the control part 30 rotates at least one of the first fan andthe second fan at a medium speed to output a medium flow rate. (S73).

Opposite to this, if it is determined that the present value ofconcentration change is lower than the third reference value, fordetermining a level of the present value of the concentration change,the control part 30 determines if the present value of concentrationchange is higher than the fourth reference value, i.e., −0.1. (S42)

As a result of this, if the present value of concentration change ishigher than the fourth reference value, the control part 30 determinesthat the present value of concentration change is medium while thepresent concentration value is low. Opposite to this, if the presentvalue of concentration change is lower than the fourth reference value,the control part 30 determines that the present value of concentrationchange is low while the present concentration value is low.

Accordingly, in this case, as shown in [Table 2] and FIG. 4, the controlpart 30 rotates at least one of the first fan and the second fan at thelowest speed to output a lowest flow rate. (S74)

In the meantime, the control part 30 repeats a process of reading ameasured value at the VOC sensor 15, and controlling the flow rate forcleaning, or ventilating the room with reference to the measured valueduring the air conditioning system is operated automatically. For this,upon finishing above process, the control part 30 determines if the airconditioning system is operated in the automatic operation mode. (S80)

As a result of the determination, if the air conditioning system is notoperated in the automatic operation mode, i.e., operated manually, orstationary, the control part 30 terminates the flow rate controlrequired for cleaning, or ventilating the room.

Opposite to this, as a result of the determination, if the airconditioning system is operated in the automatic operation mode, thecontrol part 30 determines if a preset time period is passed afterreading the measured value at the VOC sensor 15. (S90)

If the preset time period is passed, the control part 30 reads themeasured value at the VOC sensor 15 again, and performs above stepsstarting from the step S20. However, if the preset time period is notpassed, the control part 30 repeats the step S80 and the step S90 untilthe present time period is passed.

As has been described, the method for controlling an air flow rate of anair conditioning system of the present invention has the followingadvantages.

Not only absolute concentration, but also a value of concentrationchange of volatile organic compounds are taken into account incontrolling the flow rate to the air required for cleaning, orventilating the room. Therefore, in cleaning, or ventilating room air,not only a level of pollution of room air, but also rapid room airpollution is made to deal with.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. A method for controlling an air flow rate of an air conditioningsystem, comprising the steps of: (a) measuring a concentration ofvolatile organic compounds in air, periodically; (b) calculating a valueof concentration change from concentration values measured at thepresent time and in the past; and (c) controlling the flow rate of airfor cleaning or ventilating a room with reference to the presentconcentration and value of concentration change.
 2. The method asclaimed in claim 1, wherein the value of concentration change in thestep (b) is a difference of a concentration value measured at thepresent time and a concentration value measured right before.
 3. Themethod as claimed in claim 1, wherein the flow rate of the air forcleaning or ventilating a room includes a highest flow rate, a high flowrate, a medium flow rate, and a lowest flow rate.
 4. The method asclaimed in claim 3, wherein the flow rate of the air for cleaning orventilating a room is controlled to be the highest flow rate when theconcentration value is high, and the value of concentration change ishigh or medium.
 5. The method as claimed in claim 3, wherein the flowrate of the air for cleaning or ventilating a room is controlled to bethe high flow rate when the concentration value is high, and the valueof concentration change is low, or the concentration value is medium,and the value of concentration change is high.
 6. The method as claimedin claim 3, wherein the flow rate of the air for cleaning or ventilatinga room is controlled to be the medium flow rate when the concentrationvalue is medium, and the value of concentration change is medium or low,or the concentration value is low, and the value of concentration changeis high.
 7. The method as claimed in claim 3, wherein the flow rate ofthe air for cleaning or ventilating a room is controlled to be thelowest flow rate when the concentration value is low, and the value ofconcentration change is medium of low.
 8. The method as claimed in claim1, wherein the flow rate of the air for cleaning the room is controlledby controlling a rotation speed of a fan which draws air from the roomand discharges the air to the room, again.
 9. The method as claimed inclaim 1, wherein the flow rate of the air for ventilating the room iscontrolled by controlling a rotation speed of a fan which draws outdoorair and discharges the outdoor air to the room.
 10. The method asclaimed in claim 1, wherein the flow rate of the air for ventilating theroom is controlled by controlling a rotation speed of a fan which drawsroom air and discharges the room air to an outside of the room.
 11. Themethod as claimed in claim 1, wherein the step (c) includes the stepsof; (c1) determining a level of the concentration value measured at thepresent time, (c2) determining a level of the value of the concentrationchange calculated at the present time, and (c3) controlling a rotationspeed of at least one of a first fan for supplying air to the room and asecond fan for discharging air from the room with reference to thelevels of the concentration value and the value of the concentrationchange.
 12. The method as claimed in claim 11, wherein the step (c1)includes the step of comparing the measured concentration value tovarious reference values.
 13. The method as claimed in claim 11, whereinthe step (c2) includes the step of comparing the calculated value ofconcentration change to various reference values.
 14. The method asclaimed in claim 11, wherein the first fan and the second fan rotate atone of speeds inclusive of a highest speed, a high speed, a mediumspeed, and a lowest speed, respectively.
 15. The method as claimed inclaim 14, wherein the (c3) step includes the step of rotating at leastone of the first fan and the second fan at the highest speed when theconcentration value is high, and the value of the concentration changeis high or medium.
 16. The method as claimed in claim 14, wherein the(c3) step includes the step of rotating at least one of the first fanand the second fan at the high speed when the concentration value ishigh, and the value of the concentration change is low.
 17. The methodas claimed in claim 14, wherein the (c3) step includes the step ofrotating at least one of the first fan and the second fan at the highspeed when the concentration value is medium, and the value of theconcentration change is high.
 18. The method as claimed in claim 14,wherein the (c3) step includes the step of rotating at least one of thefirst fan and the second fan at the medium speed when the concentrationvalue is medium, and the value of the concentration change is medium orlow.
 19. The method as claimed in claim 14, wherein the (c3) stepincludes the step of rotating at least one of the first fan and thesecond fan at the medium speed when the concentration value is low, andthe value of the concentration change is high.
 20. The method as claimedin claim 14, wherein the (c3) step includes the step of rotating atleast one of the first fan and the second fan at the lowest speed whenthe concentration value is low, and the value of the concentrationchange is medium or low.